I too am getting this error when attempting to migrate content from our v3.7 project to a new v5.0 project. I've successfully installed the migration export service to the v3.7 application, and the connection tests successfully from the v5.0 project's migration module. However, when I attempt to either check items count or perform the migration, I am seeing the same message as displayed in Annie's screenshot above.
Was Annie's issue resolved in the aforementioned support ticket? If so, would it be possible to include the details of the resolution in this thread? Or is the information within the support ticket publicly available somewhere within this site?
Thanks in advance,